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Use the following rules in your Apache configuration (or your .htaccess file) to redirect all traffic from one domain to another. This also keeps the query string in place so that the user isn't just dumped to the homepage.

RewriteEngine on
RewriteCond %{HTTP_HOST} !^www\.example\.com$ [NC]
RewriteRule ^(.*)$ http://www.example.com%{REQUEST_URI} [L,R=301]

These rules are mod_rewrite dependent, so you'll need that module enabled in your Apache install.

To redirect from HTTPS to HTTP on the home page only using the following rule.

RewriteCond %{HTTPS} on
RewriteRule ^/?$ http://%{SERVER_NAME}/ [R=301,L]

The variable %{HTTPS} will be either "on" or "off" and will be enabled even if SSL is not installed on your site. The rule above sees that HTTPS is on and redirects the home page to the HTTP version. You can even chain lots of rules together like this.

The use of mod_rewrite on a site can have a powerful effect on search engine positioning, but to do it properly you will need to create a "slug" for each page. A slug is a lowercase alphanumeric version of the page title, with any spaces removed.

To get a slug you will need to use a function to turn a readable page title into a string that can be used as part of a URI.

Using mod_rewrite on websites is fairly straightforward and can create some lovely looking URL structures. Instead of having a URL that contains lots of odd looking parameters like this:

http://www.example.com/example.php?parameter1=value1¶meter2=value2

You can use a .htaccess file to rewrite the URL on the server side in order to shorten this to something like this:

URL canonicalisation is where you have a website with different URLs outputting the same content. When search engine spiders see all this content that is the same they can get confused as to what page to display in search engine result pages. The following URLs, although they are different, actually produce the same content.